Interannual And Seasonal Variances Of Population Biological Characteristic Of Snailfish, Liparis Tanakae In Yellow Sea

Anthropic activities such as fishing, high-density aquaculture, coastal construction,large-scale hydraulic engineering, pollutants output and biological invasions have far-reachingimpact on the marine ecosystem. They reconstructed marine habitat, reduced the age and size inpopulation, decreased the stability of population structure. Besides, climate changes and fish lifecycle were closely related, many climate index cycle were similar to the fish production changes.Younger age making the fish production fluctuates significantly by climate changes. Under thedual pressures, the dominant species in the coastal waters of China changed frequently. Anglerfishand snailfish became dominate species until the late in1990s. The marine fish family Liparidae（snailfishes） includes31genera and about more than350species. The majority of species arefound in the cold waters of North Pacific、North Atlantic and the Antarctic Oceans. In Yellow Sea,snailfish which was important food web passage has become the top predator and high status infisheries ecosystem. Research on seasonal and interannual variances in population characteristicscan provide a reference for studying the fisheries ecosystem in Yellow Sea.Seasonal variance: Distribution and biological characteristics of snailfish Liparis tanakae inthe central and southern Yellow Sea were examined based on the bottom trawl survey data inJune-August, October,2009and January, May,2010. The results showed that the average standardlength and body weight remarkably increased from spring （4.7cm,3.3g） to winter （34.2cm,764.9g）, the average standard length of male individuals were significantly larger than those offemale individuals all this year except spring. The sex ratios （:） changed with seasons andstandard length. The larger standard length, the higher proportion of male individuals, on thecontrary, the higher proportion of female individuals. The proportion of male individuals washigher in summer （0.70:1, P<0.05） and lower in autumn （1.35:1,P<0.05）. However, there was nosignificant difference in sex ratios between winter and spring. The feeding intensity was largerthan class2.5through the whole year and showed significant gender difference in spawningseason （male>female, P<0.05）, but condition factors of male individuals were lowest level. Therelative biomass increased from spring （0.17kg/h） to autumn （15.36kg/h） and decreased in winter（2.37kg/h）. The relative biomass （kg/h） and the proportion of snailfish in the total catch in summerand autumn in the present study greatly enhanced when compared with those in the correspondingseasons in2000.The snailfish mainly distributed in the sea area at7.8¹3.6℃and the salinity of32.0³3.8‰, and its average body weight was significantly related to water depth （except autumn）.According to the information on the distribution of the mature individuals, combined with thedistribution of snailfish juveniles, excluding Haizhou Bay, the deep water area in the centralYellow Sea might be the spawning ground of snailfish.Age structure:200snailfish samples collected in the Yellow Sea from January2011toMarch2012and made age determination by sagittal otolith. The standard length, body weight andsagittal otolith weight range from5.1⁵1.3cm,2.5²358g and0.4⁸.0mg respectively. Therewas gradually growth in average otolith weight from May （0.76mg） to February （6.62mg）. Length L, weight W and otolith weight W₀were best fitting in exponential: W₀=0.109L^1.095（R²=0.9,N=200）, W₀=4.93W0.359（R²=0.9, N=200）. Covariance results showed that the otolithweight in female was significantly larger than male, especially in29³9cm （P=0.01<0.05）. Theotolith Obscure might form in late autumn or early winter. The age of these snailfish ranged from0to2, sagittal otolith weight had large overlaps between0a fish and1a fish for individuals withsimilar body length, but little overlaps between1a and2a fish. It is found that larger than4.0mg ofotolith in1a fish, and greater than6.0mg in2a fish.Interannual variance: Distribution and biological characteristics of spawning population ofsnailfish L. tanakae in Yellow Sea were examined based on the bottom trawl survey data in wintersince1958. The result indicated that the frequency of occurrence（12%²6.5%） and averagerelative resource density（1.1⁴.1kg/h） were lowest in1950s,the highest were in1980s （87.5%）and93-94（15.5kg/h） respectively. Compare to other period, the distribution of snailfish migratednorthward and frequency of occurrence decreased in1990s. The frequency of occurrence andaverage relative resource density both rebounded from1999to2010. Average standard lengthdecreased since1985and more faster in recent years. The average standard length of maleindividuals were significantly larger than those of female individuals all this period except1985.There was no significant difference in sex ratios all the periods. Sexual maturity ratio （>Ⅳ） werelarger by standard length. However, it gradually smaller （51.1%²3.9%）since1985, but gonad inⅢ period percentage increase sharply（6.7%⁷1.8%）. There was highly related between averagerelative resource density and surface sea temperature in recent ten years, the lower the temperature,the higher average relative resource density.Fecundity: This studies analyzes the relationship between individual fecundity and growthindex of L. tanakae collected in1985-1986and2011-2012in the central and southern Yellow Sea.The result are summarized as follows: The individual absolute fecundity F of L. tanakae is9407～84209eggs （37677in average） in1980s,which is more than2984～81614eggs（24728in average）in2010s. The individual relative fecundity by standard length F_Lin two periods were446¹981eggs/cm�'�114¹690eggs/cm respectively, while the individual relative fecundity by bodyweight F_Wwere18¹57eggs/g�'�15¹06eggs/g. Covariance analysis indicated no significantlydifference in years. F in two periods showed positive relation in power exponent with standardlength and in linear with body weight. F_Lincreased and Fwreduced with the standard length inlinear. However, the relationship between F_L、F_Wand body weight were not obvious. The eggsize both showed doublet distribution, egg size in1980s（1.11mm） smaller than2011-2012（1.18mm）. Gonadosomatic index（GSI） and condition factor both fall in January2011compare with same time in1986, but no significant difference with the individual absolutefecundity. In addition, sexual maturity individual of another snailfish L. chefuensis reported in thisstudy. Standard length93mm; Fecundity3128; Average egg size1.08mm, doubletdistribution;According to the information on the time we collected mature individuals, spawningtime may last a long period in Yellow Sea.Primary species identification: During the survey in November2011,we found smallsnailfish individuals（<20cm） with different figure on their fins and body, such as no figure, regularor irregular spots, regular Stripe, white radial lines around eyes and so on In this study,we use thepartial sequences of mitochondrial cytochrme oxidase subunit Ⅰ （COⅠ）gene order to identify the25snailfish in different figures. The result were shown as follows. All the samples but onedetected, including22L.tanakae and2L. chefuensis。According to phylogenetic tree analysis inLiparidae species, the two snailfishes are similar to genus Liparis species. Intraspecific geneticdistance of L.tanakae was only from0.002to0.003. it is closer with three species, L. dennyi, L.gibbus and L. fucensis and their genetic distance were just0.057⁰.067. Intraspecific geneticdistance between L.tanakae and L. chefuensis is0.134. Their morphological characteristics werequite different. The largest genetic distance in Liparidae species is0.214. This study demonstratedthere were a variety of figure patterns, which can’t be used as a basis for snailfish classification,all of these provide basic information for species identification in survey.